Analog resistive touch screens are one of the most popular technologies used today in consumer electronic products such as PDAs (personal digital assistants), calculators and toys. The main reasons for this are that they are inexpensive and simple to integrate.
Resistive touch screens use ITO (Indium Tin Oxide) as a resistive element for pen/finger detection. When a pen or finger is used to press a particular location on the touch screen, this is converted into coordinates identifying the location. It is important that the coordinates accurately identify the location. Because ITO properties vary significantly over time and when exposed to temperature and humidity variation, readings of the touch screen may be converted to inaccurate coordinates thereby causing a malfunction of the product.
In order to deal with this problem, conventional resistive touch screens must be periodically manually recalibrated. A manual calibration setup menu typically asks the user to touch the four corners of the touch screen. The readings obtained for these touches are used to perform recalibration. This process must be repeated every six months or so. Unfortunately, most of the users forget to do it or do not understand well how to do it. This can result in inaccurate positioning and errors or malfunctions of the product.
U.S. Pat. No. 5,283,559 entitled "Automatic Calibration of a Capacitive Touch Screen used with a Fixed Element Flat Screen Display Panel" which issued Feb. 1, 1997 to Kalendra et al. discloses a system for recalibrating capacitive touch screens. This system is not applicable for resistive touch screens as the capacitive touch screen technology is entirely different.